Photosensitive sensing system for a currency detector



1967 F. A. LEINGANG ETAL ,30

PHOTOSENSITIVE SENSING SYSTEM FOR A CURRENCY DETECTOR Filed Sept. 5,1963 604* FIGJ.

United States Patent 3,304,432 PHOTOSENSITIVE SENSING SYSTEM FOR ACURRENCY DETECTOR Frank A. Leingang, Jennings, and William R. Cousins,St. Louis County, Mo., assignors to National Reiectors, linc., St.Louis, Mo., a corporation of Missouri Filed Sept. 5, 1963, Ser. No.306,769 14 Claims. (Cl. 250219) This invention relates to improvementsin currency detectors. More particularly, this invention relates toimprovements in currency detectors which optically sense inserted bills.

It is, therefore, an object of the present invention to provide animproved currency detector which optically senses inserted bills.

A number of currency detectors which optically sense inserted bills havebeen proposed; and some of those currency detectors have been built.Many of those currency detectors utilized lamps that were normallydeenergized and that were energized only after an inserted bill was inposition to be sensed. A normally de-energized lamp is desirable, in thesense that it keeps the photocell or photocells from receiving lightfrom those portions of a bill which are not intended to be sensed butwhich move past the photocell or photocells as the bill is moved intoposition to be sensed; but a normally deenergized lamp is undesirable,in the sense that it will not attain full brilliance immediately and inthe sense that it will have a shortened life. It would be desirable toprovide a currency detector which could optically sense inserted billsand which could have the lamp or lamps thereof energized at all times.The present invention provides such a currency detector; and it is,therefore, an object of the present invention to provide a currencydetector which optically senses inserted bills and which has the lampsthereof energized at all times.

The currency detector provided by the present invention will grip aninserted bill and will move that bill into a testing position; and lightfrom that bill will reach the photocells of that currency detector asthat bill is being so moved. However, that light will be unable to causethose photocells to initiate the acceptance of that bill until afterthat bill has been moved all the way into that testing position; becausethe currency detector of the present invention has an inhibiting circuitwhich prevents positively the acceptance of a bill until after that billhas been moved all the way into the testing position. Once the bill hasbeen moved all the way into that testing position, the inhibitingcircuit can permit the photocells to initiate the acceptance of the billif that bill is authentic, is of the proper denomination, and isproperly oriented. Specifically, if the inserted bill is authentic, isof the proper denomination, and is properly oriented as it reaches thetesting position, the photocells of the currency detector will receivethe amounts of light which they need to initiate the acceptance of thatbill. The amounts of light which those photocells receive from thatbill, as that bill is being moved into that testing position, will vary;but even if the amounts of light which the photocells receive from themoving bill should happen to equal the amount of light which thosephotocells need to initiate the acceptance of an inserted bill, theinhibiting circuit will keep those photocells from initiating the ac-"ice ceptance of the bill until after that bill has been fully movedinto the testing position. As a result, the currency detector of thepresent invention will keep portions of a bill, which are not intendedto be sensed, from initiating the acceptance of that bill even thoughthe said portions are moved past the photocells while the lamps areenergized. -It is, therefore, an object of the present invention toprovide an inhibiting circuit for a currency detector which willpositively keep the photocells of that currency detector from initiatingacceptance of a bill until after that bill has been fully moved into thetesting position.

The resistance values of commercially available photocells can varywidely, even where those photocells receive the exact same amounts oflight. It would be desirable to provide a circuit for a currencydetector which could enable that currency detector to optically sensebills with accuracy despite the inherent wide variations in theresistance values of commercially available photocells. The presentinvention provides such a circuit; and it is, therefore, an object ofthe present invention to provide a circuit for a currency detector whichcan enable that currency detector to optically sense bills with accuracydespite the inherent wide variations in the resistance values ofcommercially available photocells.

The circuit for the currency detector of the present invention connectsthe photocells of that currency detector in pairs, connects thephotocells of each pair in series, and connects a potentiometer inparallel with one photocell of each pair of photocells. Adjustment ofthe positions of the movable contacts of the potentiometers willcompensate for variations in the resistances of the photocells.Adjustment of those positions also will compensate for variations in thebrilliance of the lamps. In addition, adjustment of those positions willcompensate for variations in the characteristics of the componentsbetween the movable contacts of those potentiometers and the acceptportion of the circuit. As a result, the potentiometers of the presentinvention enable the circuit for the currency detector to operateetfectively despite variations in the resistances of the photocells, inthe brilliance of the lamps, and in the characteristics of thecomponents between the movable contacts of those potentiometers and theaccept portion of the circuit. It is, therefore, an object of thepresent invention to connect the photocells of a currency detector inpairs, to connect the photocells of each pair in series, and to connecta potentiometer in parallel with one photocell of each pair ofphotocells.

The circuit for the currency detector of the present invention has aphase inverter connected between the accept portion of that circuit andthe movable contact of each potentiometer that is connected in parallelwith a photocell; and each phase inverter will respond to apredetermined voltage at the movable contact of its potentiometer totend to initiate the acceptance of the inserted bill. However, thatphase inverter will respond to undue displacement of the voltage at thatmovable contact in a predetermined direction to prevent acceptance ofthat bill. The circuit for the currency detector also has a circuitcomponent, connected to the movable contact of each potentiometer thatis connected in parallel with a photocell, which will respond to thesaid predetermined voltage at the movable contact of its potentiometerto tend to initiate the acceptance of the inserted bill. However, thatcircuit component will respond to undue displacement of the voltage atthat movable contact in the opposite direction to prevent acceptance ofthat bill. As a result, the circuit of the present invention will tendto permit acceptance of the inserted bill if the voltage at the movablecontact of each potentiometer that is connected in parallel with aphotocell is at a predetermined value but will prevent the acceptance ofthat bill if that voltage is displaced unduly in either direction fromthat predetermined value. It is, therefore, an object of the presentinvention to provide a circuit for a currency detector which has a phaseinverter, intermediate between the accept portion of that circuit andthe movable contact of each potentiometer that is connected in parallelwith a photocell, to tend to permit acceptance of an inserted bill whenthe voltage at that movable contact is at a predetermined value and toprevent acceptance of that bill when that voltage is unduly displaced ina predetermined direction from that value, and which also has a circuitcomponent connected to the said movable contact to tend to permitacceptance of the bill when the voltage at that movable contact is atthe said predetermined value and to prevent acceptance of that bill whenthat voltage is unduly displaced in the opposite direction from thatvalue.

The inhibiting circuit for the currency detector of the presentinvention includes members, such as diodes, which can be blocked. Thosemembers will coact to permit acceptance of a bill only if all of thosemembers are subjected to voltages within a predetermined range. This isdesirable because it makes certain that a bill will be rejected if anyone of the members is not subjected to a voltage within that range. Itis, therefore, an object of the present invention to provide members,such as diodes, which can be blocked and which will coact to preventacceptance of an inserted bill unless all of those members are subjectedto voltages within a predetermined range.

Other and further objects and advantages of the present invention shouldbecome apparent from an examination of the drawing and accompanyingdescription.

In the drawing and accompanying description, a preferred embodiment ofthe present invention is shown and described but it is to be understoodthat the drawing and accompanying description are for the purpose ofillustration only and do not limit the invention and that the inventionwill be defined by the appended claims.

In the drawing, FIG. 1 is a schematic diagram of a preferred form ofcircuit for the optical sensing system of the present invention, and

FIG. 2 is a diagram showing a sub-circuit which can be substituted forany one of three sub-circuits in the circuit in FIG. 1.

Referring to FIG. 1 in detail, the numerals 206, 208, 210, 212, 514 and516 denote lamps which can be mounted in a currency detector. Whilethose lamps can be mounted in various currency detectors, those lampshave been mounted in the currency detector which is shown and describedin the commonly-assigned, co-pending application of Calvin L. Chumleyfor Currency Detectors Serial No. 306,767 which Was filed September 5,1963, now Patent No. 3,265,205. Photocells 214, 216, 218, 220, 518 and520 are located, respectively, adjacent the lamps 206, 208, 210, 212,514 and 516; and those photocells will receive light that is directedagainst an inserted bill by those lamps.

The numeral 596 denotes a conductor which will be suitably connected toa source, not shown, of positive voltage; and the numeral 604 denotes aconductor which will be suitably connected to a source, not shown, ofnegative voltage. In one preferred embodiment of the optical sensingsystem of the present invention, the source of positive voltage canprovide a regulated fifteen volts and the source of negative voltage canprovide a regulated fifteen voltage. The numeral 570 denotes a conductorwhich will be suitably connected to a source, not shown, of positivevoltage; and, in the said preferred embodiment of the optical sensingsystem of the present invention, that source will provide a voltage ofabout one hundred and fifty volts.

The numeral 624 denotes a relay coil; and the lefthand terminal of thatrelay coil is connected to conducto-r 596 by junctions 1078 and 1034, asix hundred and eighty ohm resistor 1032, and a junction 988. Therighthand terminal of that relay coil is connectable to ground by ajunction 1094, normally-open relay contacts 626, conductor 922, andnormally-open switch 444. The relay contacts 626 will close whenever therelay coil 624 is energized; and the switch 444 will be closed by a camor other device shortly after the initiation of a cycle of operation ofthe currency detector. That switch will then be kept closed untilshortly before the end of that cycle of operation.

The lower terminals of the lamps 210 and 212 are connected to theconductor 604 by junctions 930, 928, 926 and 924; and that conductorwill supply a negative fifteen volts to those lower terminals. Junctions924, 926, 932, 934, 936 and 938 connect the lower terminals of the lamps206 and 208 to the conductor 604. Junctions 924, 926, 932, 934, 940,942, 944 and 946 connect the lower terminals of the lamps 514 and 516 tothe conductor 604. The upper terminals of the lamps 514, 516, 206, 208,210 and 212 are connected to ground by junctions 962, 960, 958, 956,954, 952, 950 and 948. As a result, those lamps will be illuminatedwhenever the source of nega= tive voltage supplies fifteen volts to theconductor 604. Those lamps are preferably Sylvania E518 lamps.

The photocells 518 and 520 are connected in series between junctions 944and 962 by junction 970 and thus have fifteen volts applied across them.The photocells 214 and 216 are connected in series between the junctions936 and 956 by junction 992 and thus have fifteen volts applied acrossthem. The photocells 218 and 220 are connected between the junctions 928and 950 by junction 1012 and thus have fifteen volts applied acrossthem; The photocells 214, 216, 218, 220, 518 and 520 are preferably RCAC70306 photocells; and they will conduct current whenever the source ofnegative voltage supplies fifteen volts to the conductor 604. Theresistance of each of those photocells will increase as the amount oflight striking that photocell decreases; and, com versely, theresistance of each of those photocells will decrease as the amount oflight striking that photocell increases. The photocells 214, 218 and 518will receive light that is reflected from light areas on an authenticbill disposed within the testing area of the currency detector and thephotocells 216, 220 and 520 Willl receive light that is reflected fromdark areas on an authentic bill disposed within that testing area.

A twenty-five thousand ohm potentiometer 972 is con nected in parallelwith the photocell 520, a twenty five thousand ohm potentiometer 994 isconnected in parallel with the photocell 216, and a twenty-five thousandohm potentiometer 1014 is connected in parallel with the photocell 220.

The numeral 968 denotes a T1494 transistor which has the emitter thereofconnected to conductor 604 by a twenty-seven hundred ohm resistor 980and junctions 978, 940, 934, 932, 926 and 924. The collector of thattransistor is connected to the conductor 596 by a junctron 982, a twelvethousand ohm resistor 984, and junctrons 986 and 988. The base of thattransistor 968 is connected to the movable contact of potentiometer 972gyfisan eighteen hundred ohm resistor 976 and a junction The numeral 990denotes a second TI494 transistor; and that transistor has the emitterthereof connected to the conductor 604 by a twenty-seven hundred ohmresrstor 1002 and junctions 1000, 932, 926 and 924. The

collector of that transistor is connected to the conductor 596 by ajunction 1004, a twelve thousand ohm resistor 1006, and junctions 1008,986 and 988. The base of that transistor is connected to the movablecontact of potentiometer 994 by an eighteen hundred ohm resistor 998 anda junction 996.

The numeral 1010 denotes a third T1494 transistor; and the emitter ofthat transistor is connected to the conductor 604 by a twenty-sevenhundred ohm resistor 1024 and junctions 1022, 1020 and 924. Thecollector of that transistor is connected to the conductor 596 byjunction 1026, a twelve thousand ohm resistor 1028, and junctions 1008,986 and 988. The base of that transistor is connected to the movablecontact of potentiometer 1014 by an eighteen hundred ohm resistor 1018and a junction 1016.

The numeral 1030 denotes a fourth T1494 transistor; and the emitter ofthat transistor is connected to the conductor 604 by a junction 1040, aneight hundred and twenty ohm resistor 1042, and junctions 1044, 1022,1020 and 924. The collector of that transistor is connected to theconductor 596 by a junction 1038, a fifteen hundred ohm resistor 1036,junction 1034, resistor 1032, and junction 988.

A one hundred thousand ohm resistor 966 is connected to the conductor604 by a junction 964, a thirtythree thousand ohm resistor 967, andjunctions 942, 940, 934, 932, 926 and 924. The resistor 966 also isconnected to the conductor 604 by junction 964, a Zytan diode 1052, aconductor 1050, junctions 1056, 1058 and 1048, a ten thousand ohmresistor 1046, the base-emitter circuit of transistor 1030, junction1040, resistor 1042, and junctions 1044, 1022, 1020 and 924.

The collector of transistor 968 is connected to conductor 1050 byjunction 982, a Zytan diode 1054, and junction 1056. The junction 974 isconnected to conductor 1050 by a Zytan diode 1060 and junction 1058. Thecollector of transistor 990 is connected to conductor 1050 by junction1004, a Zytan diode 1062, and junction 1064. The junction 996 isconnected to conductor 1050 by a Zytan diode 1068 and junction 1066. Thecollector of transistor 1010 is connected to conductor 1050 by junction1026, a Zytan diode 1072, and junction 1070. The junction 1016 isconnected to conductor 1050 by a Zytan diode 1074.

The numeral 1076 denotes a fifth TI494 transistor; and the emitter ofthat transistor is connected to conductor 604 by junction 1040, resistor1042, and junctions 1044, 1022, 1020 and 924. The collector of thattransistor is connected to conductor 596 by junctions 1082 and 1094,relay coil 624, junctions 1078 and 1034, the six hundred and eighty ohmresistor 1032, and junction 988. The base of that transistor isconnected to'the movable contact of a five thousand ohm potentiometer1088; and the upper terminal of that potentiometer is connected to thecollector of transistor 1030 by junction 1086, a twelve thousand ohmresistor 1084, and junction 1038. The lower terminal of thatpotentiometer is connected to the junction 1044 by a forty-seven hundredohm resistor 1092. A shunt 1090 is connected between the upper terminaland the movable contact of the potentiometer 1088 by the junction 1086.The transistors 1030 and 1076 and the resistors associated with themconstitute a Schmitt trigger. While a Schmitt trigger is very desirable,because of its rapid switching action, other flipflop circuits could beused in lieu of the Schmitt trigger shown in the drawing.

The numeral 1080 denotes a Zytan diode which has the anode thereofconnected to the right-hand terminal of the relay coil 624 by junctions1082 and 1094 and which has the cathode thereof connected to theleft-hand terminal of that relay coil by junction 1078.

The upper terminal of the resistor 966 is connected to the conduct-or570 by a sixty-eight thousand ohm resistor 788; and that upper terminalis selectively conbill, receive no light from its associated lamp.

nectable to ground by a switch 790, a resistor 791, and a conductor 792.While that switch is shown in FIG. 1 as a single pole single throwswitch, that switch will preferably by a thyratron, as shown by the saidChurnley application; and, whenever that thyratron is nonconductive, itwill, effectively, serve as an open switch. However, when that thyratronfires, it will effectively serve as a closed switch and will connect theupper terminal of resistor 966 to ground via the resistor 791 andconductor 792. The resistor 791 is intended to represent the relativelylow plate-to-cathode resistance of the thyratron after that thyratronhas been fired. With the exception of the switch 444, the switch 790,and the resistor 791, the components in FIG. 1 are identical to thesimilarly-numbered components in the said Churnley application.

The lamps 206, 208, 210, 212, 514 and 516 could be so related to thephotocells 214, 216, 218, 220, 518 and 520 that each photocell would,prior to the insertion of a bill, receive light from its associatedlamp. On the other hand, those lamps could be so related to thosephotocells that each photocell would, prior to the insertion of a Ifdesired, some of those photocells could be arranged to receive lightfrom their associated lamps while the rest of those photocells receivedno light from their associated lamps prior to the insertion of a bill.In the currency detector of the said Churnley application, the lamps 206and 514 are mounted so the light from the lamp 206 will be directedtoward the lamp 514, and vice versa; and hence substantially no lightwill initially fall upon the photocells 214 and 518. Light from the lamp208 will initially fall upon the lamp 516, and vice versa; and hence thephotocells 216 and 520 will receive substantially no light prior to theinsertion of a bill into the currency detector. Light from the lamp 210will initially be directed away from the photocell 218; and hence thatphotocell will receive substantially no light until a bill is inserted.However, a substantial amount of light will pass from the lamp 212 tothe photocell 220 before a bill is inserted. This means that until abill is inserted in the currency detector, the photocells 214, 218 and518 will receive substantially no light; although those photocells willreceive substantial amounts of light from an inserted bill if that billis authentic and of the proper denomination. Until a bill is inserted inthe currency detector, the photocells 216 and 520 also will receivesubstantially no light; although those photocells will receive somelight from an inserted bill if that bill is authentic and of the properdenomination. Until a bill is inserted in the currency detector,photocell 220 will receive a substantial amount of light; although thatphotocell will receive only a little light from an inserted bill if thatbill is authentic and of the proper denomination. The optical sensingsystem of FIG. 1 will be set to permit the transistor 1030 to berendered non-conductive only when the photocells 214, 218 and 518receive substantial amounts of light and the photocells 216, 220 and 520receive only small amounts of light; and hence that sensing system willnot permit that transistor to become non-conductive whenever thecurrency detector is at rest.

In setting the optical system of FIG. 1, the movable contact ofpotentiometer 1088 will initially be moved down to the lower end of thatpotentiometer to make sure that the transistor 1076 will benon-conductive. Also, the switch 790 will be closed; and, where thatswitch is a thyratron, that thyratron will be suitably renderedconductive, as by reducing the negative bias on the control grid of thatthyratron. As long as the switch 790 is open, current will flow fromconductor 570 via resistors 788 and 966, junction 964, resistor 967, andjunctions 942, 940, 934, 932, 926 and 924 to the conductor 604; and thatflow of current will enable the resistors 788, 966 and 967 to establisha positive voltage of about five volts at the junction 964. However,whenever the switch 790 is closed, current also will flow from conductor570 via resistor 788, switch 790, resistor 791, and conductor 792; andthe resistance of resistor 792 will be so small that the voltage at thejunction 964 will become negative and will be greater than eight andone-half volt. Once the switch 790 has been closed, an authentic bill ofthe proper denomination, with average cleanness and light reflectivity,will be set in the testing area of the currency detector.

At this time, a DC. voltmeter will be connected between junctions 982and 924, and the movable contact of potentiometer 972 will be moved toprovide a minimum reading on that voltmeter. The settings of the movablecontacts of potentiometers 994 and 1014 are not significant while thevoltmeter is so connected; and hence those movable contacts can haverandom settings. Once the movable contact of potentiometer 972 has beenset to establish a minimum voltage between junctions 982 and 924, thevoltmeter will be connected between junctions 1004 and 924; and then themovable contact of potentiometer 994 will be moved to provide a minimumreading on that voltmeter. The setting of the movable contact ofpotentiometer 1014 is not significant while the voltmeter is soconnected; and hence that movable contact can have a random setting.After a minimum voltage has been established between junctions 1004 and924, the voltmeter will be connected between junctions 1026 and 924; andthen the movable contact of potentiometer 1014 will be moved to providea minimum reading on that voltmeter. Once that minimum reading has beenestablished, the movable contact of potentiometer 1014 will be shifteduntil the reading on the voltmeter increases by about one to about oneand two-tenths volts. At this time, the movable contact of potentiometer1088 will be moved upward just far enough to render transistor 1076conductive. Thereafter, the switch 790 will be re-opened, and thevoltage at the junction 964 will become about five volts positive.Current will then flow from conductor 570 via resistors 788 and 966,junction 964, diode 1052, conductor 1050, junctions 1056, 1958 and 1048,resistor 1046, the baseemitter circuit of transistor 1030, junction1040, resistor 1042, and junctions 1044, 1022, 1020 and 924 to theconductor 604. The resulting flow of current through the base-emittercircuit of transistor 1030 will render that transistor conductive; and,as that transistor becomes conductive, the transistor 1076 will againbecome non-conductive. Thereupon, the voltmeter will again be connectedbetween junctions 1026 and 924; and the movable contact of potentiometer1014 will again be moved to provide a minimum reading on that voltmeter.At this time, the optical sensing system of FIG. 1 will be properly set;and the inserted bill will be removed.

The offsetting of the movable contact of potentiometer 1014, and thesetting of the movable contact of potentiometer 1088 while the formermovable contact is 011- set, make it possible for the currency detectorto accept authentic bills which have values of cleanness and lightreflectivity that are greater or less than average but that fall withina pre-determined range, and to reject all bills with values of cleannessand light reflectivity outside of that range.

With no bill in the testing area of the currency detector, thephotocells 518 and 520 will establish a negative voltage of about fourvolts at the junction 970; and a negative voltage of less than seven andeight-tenths volts will appear at the junction 974. Because the junction1044 is fifteen volts negative, current will tend to flow from groundvia junction 962, photocell 518, junction 970, the upper section ofpotentiometer 972, junction 974, diode 1060, junctions 1058 and 1048,resistor 1046, baseemitter circuit of transistor 1030, junction 1040,resistor 1042, and junctions 1044, 1022, 1020 and 924 to conductor 604and such a flow of current would keep that transistor conductive.

The negative voltage at the junction 974 will be more positive than thenegative fifteen volts at junction 978; and hence current will flow fromground via junction 962, photocell 518, junction 970, the upper sectionof potentiometer 972, junction 974, resistor 976, the baseemittercircuit of transistor 968, resistor 980, and junctions 978, 940, 934,932, 926 and 924 to the conductor 604. That flow of current will rendertransistor 968 conductive. The resulting current fiow from the conductor596 via junctions 988 and 986, resistor 984, junction 982, transistor968, resistor 980, and junctions 978, 940, 934, 932, 926 and 924 to theconductor 604 Will provide a negative voltage at the junction 982 whichis greater than eight volts. Such a voltage is too negative to causecurrent to flow through the base-emitter circuit of transistor 1030; andhence the voltage at junction 982 will tend to permit transistor 1030 tobecome non-conductive. However, because the voltage at junction 974 issufficiently positive to tend to cause current to flow through thebase-emitter circuit of transistor 1030, the negative voltage atjunction 982 can not cause the transistor 1030 to become non-conductive.

With no bill in the testing area of the currency detector, thephotocells 214 and 216 will establish a negative voltage of about sevenand one-half volts at the junction 992; and a negative voltage of morethan seven and eight-tenths volts will appear at the junction 996.Because the junction 1000 is fifteen volts negative, current will tendto flow from ground via junctions 962, 960, 958 and 956, photocell 214,junction 992, the upper section of potentiometer 994, junction 996,resistor 998, the base-emitter circuit of transistor 990, resistor 1002,and junctions 1000, 932, 926 and 924 to conductor 604. If the voltage atthe base of transistor 990 is not too negative, that transistor will beslightly conductive; but if that voltage is about nine volts negative,that transistor will be biased beyond cut-off. If the transistor 990 isconductive, current will flow from the conductor 596 via junctions 988,986 and 1008, resistor 1006, junction 1004, transistor 990, resistor1002, and junctions 1000, 932, 926 and 924 to the conductor 604 and makethe junction 1004 more positive than minus eight volts. If thetransistor 990 is biased beyond cut-off, the voltage at junction 1004will be even more positive. Because the junction 1044 is fifteen voltsnegative, current will tend to flow from the conductor 596 via junctions988, 986 and 1008, resistor 1006, junction 1004, diode 1062, junctions1064 and 1048, resistor 1046, the base-emitter circuit of transistor1030, junction 1040, resistor 1042, and junctions 1044, 1022, 1020 and924 to the conductor 604; and such a flow of current would keep thattransistor conductive.

The negative voltage at the junction 996 is too negative to causecurrent to flow through the base-emitter circuit of transistor 1030; andhence the voltage at junction 996 will tend to permit that transistor tobecome non-conductive. However, because the voltages at junctions 974and 1004 are sufiiciently positive to tend to cause current to flowthrough the base-emitter circuit of transistor 1030, the negativevoltage at junction 996 can not cause the transistor 1030 to becomenon-conductive.

With no bill in the testing area of the currency detector, thephotocells 218 and 220 will establish a negative voltage of about tenvolts at the junction 1012; and

a negative voltage of more than ten volts Will appear at the junction1016. As a result, the transistor 1010 will be biased beyond cut-off;and hence the voltage at junction 1026 will be more positive than minuseight volts. Because the junction 1044 is fifteen volts negative,current will tend to flow from the conductor 596 via junctions 988, 986and 1008, resistor 1028, junction 1026, diode 1072, junctions 1070,1066, 1064 and 1048, resistor 1046, the base-emitter circuit oftransistor 1030, junction 1040, resistor 1042, and junctions 1044, 1022,

swam

9 1020 and 924 to the conductor 604; and such a fiow of current wouldkeep that transistor conductive.

The negative voltage at the junction 1016 is too negative to causecurrent to flow through the base-emitter circuit of transistor 1030; andhence the voltage at junction 1016 will tend to permit that transistorto become non-conductive. However, because the voltages at junctions974, 1004 and 1026 are sufficiently positive to tend to cause current toflow through the base-emitter circuit of transistor 1030, the negativevoltage at junction 1016 can not cause the transistor 1030 to becomenon-conductive.

Also, with no bill in the testing area of the currency detector, theswitch 790 will be open, and the voltage at the junction 964 will bepositive and will have a value of about five volts. If that voltage ismore positive than the voltages at the anodes of diodes 1060, 1062 and1072, it will block those diodes; and it will also cause current to flowthrough the base-emitter circuit of transistor 1030, thereby keepingthat transistor conductive. All of this means that while the photocells214, 216, 218, 220, 518 and 520 coact, when no bill is present in thetesting area of the currency detector, to establish voltages at juctions932, 996 and 1016 which would tend to permit the transistor 1030 tobecome non-conductive, those photocells also coact to establish voltagesat junctions 974, 1004 and 1026 which would tend to keep the transistor1030 conductive; and the switch 790 establishes a positive voltage atjunction 964 which also tends to keep that transistor conductive.

When an authentic bill of the proper denomination is properly disposedwithin the testing area of the currency detector, the photocells 518 and520 will coact to develop a negative voltage of about seven andeight-tenths volts at junction 974, the photocells 214 and 216 willcoact to develop a similar voltage at junction 996, and the photocells218 and 220 Will coact to develop a similar voltage at the junction1016. The transistors 960, 990 and 1010 will respond to those voltagesto develop negative voltages of about eight volts at the junctions 982,1004 and 1026; and the resulting voltages at the anodes of diodes 1054,1060, 1062, 1068, 1072 and 1074 will be sufficiently negative to tend tocause the transistor 1030 to become non-conductive. However, until theswitch 790 is closed to permit the voltage at the junction 964 to becomenegative and to have a value greater than eight volts, the positivevoltage at junction 964 will keep current flowing through thebase-emitter circuit of the transistor 1030 and will thus keep thattransistor conductive.

If a bill, which is inserted in the currency detector, causes too muchlight to strike photocell 518, the resistance of that photocell will betoo low, and the voltage at junction 974 will be more positive thanminus seven and eight-tenths volts. That voltage will tend to causecurrent to flow through the base-emitter circuit of transistor 1030 andthereby keep that transistor conductive. However, if the inserted billcauses the photocell 518 to receive too little light, the resistance ofthat photocell Will be too high; and the voltage at junction 974 will bemore negative than minus seven and eight-tenths volts. The undulynegative voltage at junction 974 will make transistor 968 lessconductive; and hence the voltage at junction 982 will be more positivethan minus eight volts. That voltage will tend to cause current to flowthrough the base-emitter circuit of transistor 1030 and thereby keepthat transistor conductive.

If an inserted bill causes photocell 520 to receive too little light,the resistance of that photocell will be too high and will make thevoltage at junction 974 more positive than minus seven and eight-tenthsvolts. That voltage will tend to cause current to flow through thebase-emitter circuit of transistor 1030 and thereby keep that transistorconductive. However, if the inserted bill causes photocell 520 toreceive too much light, the resistance of that photocell will be too lowand will make the voltage at junction 974 more negative than minus sevenand eight-tenths volts. The transistor 968 will respond to the undulynegative voltage at the base thereof to become less conductive; and thevoltage at junction 982 will become more positive than minus eightvolts. That voltage will tend to cause current to flow through thebase-emitter circuit of transistor 1030 and thereby keep that transistorconductive.

This means that if photocell 518 receives too much light or if photocell520 receives too little light, the voltage at the movable contact ofpotentiometer 972 will be sufficiently positive to tend to cause currentto flow through diode 1060 and the base-emitter circuit of transistor1030. That current will keep that transistor conductive even if theother two pairs of photocells receive the correct amount of light andeven if the switch 790 is closed. If photocell 518 receives too littlelight or if photocell 520 receives too much light, transistor 968 willbecome less conductive and the voltage at the collector of thattransistor will be sufiiciently positive to tend to cause current toflow through diode 1054 and the base-emitter circuit of transistor 1030.That current will keep that transistor conductive even if the other twopairs of photocells receive the correct amount of light and even if theswitch 790 is closed.

It will thus be apparent that the photocells 518 and 520, the transistor968 and the diodes 1054 and 1060 coact to provide a dual action.Specifically, if those photocells cause the voltage at the movablecontact of potentiometer 972 to become unduly positive, current willtend to flow through diode 1060 and the base-emitter circuit oftransistor 1030 and keep that transistor conductive. On the other hand,if those photocells make the voitage at the movable contact ofpotentiometer 972 unduly negative, the transistor 963 will make thevoltage at the collector thereof unduly positive; and current will tendto flow through diode 1054 and the base-emitter circuit of transistor1030 and keep the latter transistor conductive.

The photocells 214 and 216, the transistor 990, and the diodes 1062 and1068 will operate in the manner in which the photocells 518 and 520, thetransistor 968, and the diodes 1054 and 1060 operate. Specifically, ifthe photocell 214 receives too much light or if the photocell 216receives too little light, the voltage at the movable contact ofpotentiometer 994 will become unduly positive; and current will tend toflow through diode 1068 and the base-emitter circuit of transistor 1030and thereby keep that transistor conductive. On the other hand, if thephotocell 214 receives too little light or if the photocell 216 receivestoo much light, the voltage at junction 996 will become unduly negativeand transistor 990 will become less conductive and will make the voltageat the collector thereof unduly positive. That voltage will tend tocause current to flow through diode 1062 and the base-emitter circuit oftransistor 1030, and keep that transistor conductive.

The photocells 218 and 220, the transistor 1010, and the diodes 1072 and1074 also will operate in the manner in which the photocells 518 and520, the transistor 968, and the diodes 1054 and 1060 operate.Specifically, if the photocell 218 receives too much light or if thephotocell 220 receives too little light, the voltage at junction 1016will become unduly positive; and current will tend to flow through diode1074 and the base-emitter circuit of transistor 1030 and thereby keepthat transistor conductive. On the other hand, if the photocell 218receives too little light or the photocell 220 receives too much light,the voltage at junction 1016 will be unduly negative and transistor 1010will become less conductive and will make the voltage at the collectorthereof unduly positive. That volt-age will tend to cause current toflow 11 through diode 1072 and the base-emitter circuit of transistor1030 and thereby keep that transistor conductive. If more than onephotocell receives too much light or if more than one photocell receivestoo little light, the diode which has the least negative voltage on theanode thereof will tend to become conductive and will tend to causecurrent to flow through the base-emitter circuit of transistor 1030 andkeep that transistor conductive.

The resistance values of commercially-available photocells tend to varyrather widely; and hence the resistance values of photocells 214, 216,218, 220, 518 and 520 could vary Widely even if all of those photocellsreceived the exact same amount of light. Furthermore, widely differingamounts of light are reflected onto the various photocells 214, 216,218, 220, 518 and 520 from an authentic bill. However, by pairing thephotocells, by connecting the photocells of each pair in series, and byconnecting a potentiometer in parallel with one photocell of each pairof photocells, the present invention can fully compensate for inherentdifferences in the resistances of the various photocells. Also, bypairing the photocells, by connecting the photocells of each pair inseries, and by connecting a potentiometer in parallel with one photocellof each pair of photocells, the present invention enables adjustment ofthe movable contact of that potentiometer to compensate for variationsin the brilliance of the lamps and for variations in the characteristicsof the transistor and resistors associated with that movable contact.

In the operation of the currency detector with which the optical sensingsystem of the present invention is used, the switch 444 will be closed;and that switch will be closed prior to the closing of switch 790 and itwill remain closed after the switch 790 is closed. Also, a bill will bemoved into the testing area; and, as that bill moves into that testingarea, that bill will interrupt the light beams from the lamps 206, 208,210, 212, 514 and 516 and will cause the light from those lamps toreflect, respectively, onto the photocells 214, 216, 218, 220, 518 and520. The amount of light that is reflected onto those photocells willvary as the light and dark portions of the upper and lower faces of thebill pass through the beams of light from these lamps; and hence theresistances of those photocells will vary. However, even if, while abill is being moved toward and into the testing area, some combinationor combinations of light and dark areas on the faces of that billhappened to cause negative voltages, equal to or greater than seven andeight-tenths volts, to appear at the anodes of all of the diodes 1054,1060, 1062, 1068, 1072 and 1074, the transistor 1030 would still notbecome non-conductive. As pointed out hereinbefore, the current whichwill flow from the conductor 570 via resistors 788 and 966, junction964, resistor 967, and junctions 942, 940, 934, 932, 926 and 924 to theconductor 604 will maintain a positive voltage of about five volts atthe junction 964; and the resulting flow of current through thebase-emitter circuit of transistor 1030 will keep that transistorconductive. This is desirable, because it obviates all need of keepingthe lamps off until after the inserted bill has been fully moved intothe testing area.

As the bill is fully moved into the testing area, the light which isreflected from the faces of that bill onto the photocells 214, 216, 218,220, 518 and 520 will cause the voltages at the anodes of all of thediodes 1054, 1060, 1062, 1068, 1072 and 1074 to be negative and to equalor exceed seven and eight-tenths volts. However, because the switch 790will still be open, the voltage at the junction 964 will still be aboutplus five volts; and the resulting current flow through the base-emittercircuit of transistor 1030 will keep that transistor conductive. Thismeans that even though the optical sensing system of FIG. 1 tends toinitiate an accept signal by tending to render the transistor 1030non-conductive, that transistor cannot become conductive until both thatsystem and the 12 switch 790 simultaneously tend to render thetransistor 1030 non-conductive.

During the operation of the currency detector with which the opticalsensing system of the present invention is used, the switch 790 will beclosed after the inserted bill has been fully moved into the testingarea. In the currency detector of the said Chumley application theswitch 790 is a thyratron, and that thyratron is fired if the magnetichead and the magnetic sensing system determine that the inserted bill isauthentic and has the desired denomination. However, the switch 790could be a billactuated switch which is to be actuated by the leadingedge of the bill as that bill reaches the testing area, or it could be arelay contact which was closed as a result of some test made on the billby the currency detector. Also, if desired, the switch 7 could be closedby a motordriven cam or some other timing device. In any event, thecurrency detector will be arranged so the switch 790 will be closedafter the inserted bill has been fully moved into the testing area andbefore the end of the cycle of operation of the currency detector. Asthat switch is closed, a low resistance path will be established betweenthe resistor 788 and ground via the resistor 791 and conductor 792; andthe voltage at the junction 964 will fall until it is negative and has avalue in excess of eight volts. Since the lamps and photocells and thecircuitry of FIG. 1 previously established, and will be maintaining,negative voltages at the anodes of diodes 1054, 1060, 1062, 1068, 1070and 1074 which exceed seven and onehalf volts, the drop in voltage atthe junction 964 will enable the voltage at the junction 1048 to becomenegative and to have a value equal to or in excess of seven and one-halfvolts. Thereupon the conductivity of transistor 1030 will decrease.

As the transistor 1030 becomes less conductive, current will flow fromthe conductor 596 via junction 988, resistor 1032, junction 1034,resistor 1036, junction 1038, resistor 1084, junction 1086, shunt 1090,the movable contact of potentiometer 1088, the base-emitter circuit oftransistor 1076, junction 1040, resistor 1042, and junctions 1044, 1022,1020 and 924 to the conductor 604. The transistor 1076 will respond tothat flow of current to become conductive; and, because the transistors1030 and 1076 and the associated resistors constitute a Schmitt trigger,the transistor 1030 will immediately become nonconductive and thetransistor 1076 will immediately start conducting heavily. Thereupon,current will flow from the conductor 596 via junction 988, resistor1032, junctions 1034 and 1078, relay coil 624, junctions 1094 and 1082,transistor 1076, junction 1040, resistor 1042, and junctions 1044, 1022,1020 and 924 to the conductor 604. The resulting flow of current willenergize relay coil 624; and that relay coil will close the contacts 626and thereby establish a holding circuit for that relay coil. Thatholding circuit extends from the conductor 596 via junction 988,resistor 1032, junctions 1034 and 1078, relay coil 624, junction 1094,contacts 626, conductor 922, and switch 444 to ground; and that holdingcircuit will keep that relay coil energized as long as the switch 444remains closed. The relay coil 624 will close other contacts, not shown,which will cause the bill to be moved to the cash box and which willcause the desired change, merchandise or service to be dispensed orvended.

Shortly before the end of the cycle of operation of the currencydetector, the switch 444 will be re-opened; and, thereupon, the holdingcircuit for the relay coil 624 will be interrupted. As that relay coilbecomes de-energized, the contacts 626 will re-open. The diode 1080 willprovide a discharge path for the inductive energy that was stored withinthe relay coil 624 while that coil was energized. Specifically, as thecontacts 626 re-open, current will fiow from the right-hand terminal ofrelay coil 624 via junctions 1094 and 1082, diode 1080, and junction1078 to the left-hand terminal of that relay coil. The impedance of thepath through that diode will be so small 13 that substantially nocurrent will tend to flow through the transistor 1076; and, in this way,the diode 1080 will protect the transistor 1076 from hurtful currentsurges when the relay coil 624 is de-energized.

During the cycle of operation of the currency detector, the bill wasmoved into the testing area and was optically sensed. The opticalsensing system determined that the bill Was acceptable; and, as theswitch 790 was closed, caused the transistor 1030 to becomenon-conductive. Thereupon, the transistor 1076 became conductive andenergized the relay coil 624; and that relay coil caused the dispensingor vending of the desired change, merchandise or service. Thereafter,the currency detector completed its cycle of operation and re-opened theswitches 790 and 444, in readiness for the insertion of another bill.

If a spurious bill or an authentic bill of an undesired denomination isinserted or if an authentic bill of the desired denomination iimproperly oriented in the testing area, the optical sensing systemshould not coact with the switch 790 to render the transistor 1030non-conductive. If the bill is an authentic bill of an undesireddenomination, or if the bill is authentic and of the desireddenomination but has the green-ink face thereof up, the amount of lightreflected onto the photocells 214, 216, 218, 220, 518 and 520 will beunable to cause the voltages at the anodes of all of the diodes 1062,1068, 1072, 1074, 1054 and 1060 to be negative and to have values equalto or greater than seven and eight'tenths volts. Instead, the lightfalling upon those photocells will cause the voltage at the anode of atleast one of those diodes to be more positive than negative seven andeight-tenths volts. Where that occurs, the optical sensing system willbe capable of holding the voltage at the junction 1048 more positivethan the negative seven and one-half volts needed to render thetransistor 1030 non-conductive. Consequently, the transistor 1076 willnot be able to become conductive and will thus not be able to energizethe relay coil 624. Because that relay coil will not be energized, thecurrency detector will not dispense or vend the desired change,merchandise or service. Instead, that currency detector will return theinserted bill to the patron and will restore the components thereof totheir normal positions in readiness for the insertion of another bill.

Referring particularly to FIG. 2, the numeral 1200 denotes apotentiometer which can be substituted for any of the potentiometers972, 994 and 1014 of FIG. 1. The numeral 1204 denotes T I494 transistorwhich can be substituted for any one of the transistors 960, 990 and1010 of FIG. 1. A junction 1202 and a resistor 1206 connect the movablecontact of the potentiometer 1200 with the base of the transistor 1204;and that junction and resistor can be substituted for any one ofjunctions 974, 996 and 1016 and resistors 976, 998 and 1010 of FIG. 1.The emitter of transistor 1204 is connected to the lower terminal ofpotentiometer 1200 by a resistor 1216 and a junction 1220; and thatresistor and junction can be substituted for any one of resistors 900,1002 and 1204 and junctions 978, 1000 and 1020 of FIG. 1. A junction1210 connects a resistor 1212 with the collector of the transistor 1204;and that junction and that resistor can be substituted for any one ofjunctions 982, 1004 and 1026 and resistors 984, 1006 and 1028 of FIG. 1.The junction 1210 also is connected to the anode of a diode 1214; andthat diode can be substituted for any one of diodes 1054, 1062 and 1072of FIG. 1. The only differences between the sub-circuit of FIG. 2 andany of the corresponding sub-circuits of FIG. 1 are the connections forthe diode 1208 in FIG. 2. That diode is identical to the dides 1060,1068 and 1074 of FIG. 1, and it has its anode connected in the same wayin which the anodes of those diodes are connected; but, instead ofhaving its cathode directly connected to the left-hand terminal ofresistor 1046, diode 1208 has its cathode connected to that terminal byjunction 1210 and diode 1214.

If it is assumed that the sub-circuit of FIG. 2 is substituted for thatsub-circuit of FIG. 1 which includes the potentiometer 972 and thetransistor 968, the photocells 518 and 520 will establish a negativevoltage of about four volts at the upper end of the potentiometer 1200until a bill is inserted in the currency detector. Such a voltage willcause a negative voltage of less than seven and eight-tenths volts toappear at the junction 1202; and, because the junction 1044 is fifteenvolts negative, current will tend to flow from ground via junction 962,photocell 518, junction 970, the upper section of potentiometer 1200,junction 1202, diode 1208, junction 1210, diode 1214, junctions 1056 and1048, resistor 1046, the base-emitter circuit of transistor 1030,junction 1040, resistor 1042, and junctions 1044, 1022, 1020 and 924 tothe conductor 604. Such a flow of current would keep that transistorconductive and prevent energization of the relay coil 624.

The negative voltage at the junction 1202 will also be more positivethan the negative fifteen volts at junction 1220; and hence current willflow from ground via junction 962, photocell 518, junction 970, theupper section of poteniometer 1200, junction 1202, resistor 1206, thebase-emitter circuit of transistor 1204, resistor 1216, and junctions1220, 940, 934, 932, 926 and 924 to the conductor 604. That flow ofcurrent would, if the diode 1208 was not connected between junctions1202 and 1210 and if that diode was not conductive, cause the transistor1204 to become sufiiciently conductive to make the voltage at junction1210 negative with a value greater than eight volts. Such a voltage atthat junction would tend to render the transistor 1030 non-conductive;but, because diode 1208 is connected between junctions 1202 and 1210 andbecause that diode is conductive, the voltage at the junction 1210 willbe just slightly less positive than the voitage at the junction 1202. Asa result, the voltage at the junction 1210 will be sufficiently positiveto cause current to flow from conductor 596 via junctions 988 and 986,resistor 1212, junction 1210, diode 1214, junctions 1056 and 1048,resistor 1046, the base-emitter circuit of transistor 1030, junction1040, resistor 1042, and junctions 1044, 1022, 1020 and 924 to theconductor 604; and that flow of current will keep the transistor 1030conductive.

When an authentic bill is moved into the testing area of the currencydetector, photocells 518 and 520 will coact to develop a negativevoltage of about seven and eighttenths volts at the junction 1202; andtransistor 1204 will respond to that voltage to develop a negativevoltage of about eight volts at the junction 1210'. The latter voltagewill tend to make the voltage at junction 1048 so negative as to renderthe transistor 1030 non-conductive. Also, the voltage at junction 1202will be so close to the voltage at junction 1210 that current will nottend to flow from junction 1202 via diodes 1208 and 1214 and thebaseemitter circuit of the transistor 1030. Consequently, thesub-circuit of FIG. 2 will, when an authentic bill is moved into thetesting area of the currency detector, tend to permit the transistor1030 to become non-conductive.

If a bill, which is inserted in the testing area of the currencydetector, causes too much light to strike photocell 518, the resistanceof that photocell will be too low; and the voltage at junction 1202 willbe more positive than minus seven and eight-tenths volts. That voltagewill tend to cause current to flow from ground via junction 962,photocell 518, junction 970, the upper section of potentiometer 1200,junction 1202, diode 1208, junction 1210, diode 1214, junctions 1056 and1048, resistor 1046, the base-emitter circuit of transistor 1030,junction 1040, resistor 1042, junctions 1044, 1022, 1020 and 924 to theconductor 604; and that current flow will tend to keep the transistor1030 conductive. However, if the inserted bill causes the photocell 518to receive too little light, the resistance of that photocell will betoo high; and the voltage at junction 1202 will be more negative thanminus seven and eight-tenths volts. The unduly negative voltage atjunction 1202 will make the transistor 1204 less conductive; and hencethe voltage at the junction 1210 will be more positive than minus eightvolts. That voltage will tend to cause current to fiow from theconductor 596 via junctions 988 and 986, resistor 1212, junction 1210,diode 1214, junctions 1056 and 1048, resistor 1046, the base-emittercircuit of transistor 1030, junction 1040, resistor 1042, and junctions1044, 1022, 1020 and 924 to the conductor 604; and that current flowwill tend to keep the transistor 1030' conductive.

If an inserted bill causes the photocell 520 to receive too littlelight, the resistance of that photocell will be too high; and will makethe voltage at junction 1202 more positive than minus seven andeight-tenths volts. That voltage will tend to cause current to flow fromground via junction 962, photocell 518, junction 970, the upper sectionof potentiometer 1200, junction 1202, diode 1208, junction 1210, diode1214, junctions 1056 and 1048, resistor 1046, the base-emitter circuitof transistor 10'30, junction 1040, resistor 1042, junctions 1044, 1022,1020 and 924 to the conductor 604; and that current flow will tend tokeep that transistor 1030 conductive. However, if the inserted billcauses photocell 520 to receive too much light, the resistance of thatphotocell will be too low; and will make the voltage at junction 1202more negative than minus seven and eight-tenths volts. The undulynegative voltage at junction 1202 will make the transistor 1204 lessconductive; and hence the voltage at the junction 1210 will be morepositive than minus eight volts. That voltage will tend to cause currentto flow from the conductor 596 via junctions 988 and 986, resistor 1212,junction 1210, diode 1214, junctions 1056 and 1048, resistor 1046, thebase-emitter circuit of transistor 1030, junction 1040, resistor 1042,and junctions 1044, 1022, 1020 and 924 to the conductor 604; and thatcurrent flow will tend to keep the transistor 1030 conductive.

This means that if photocell 518 receives too much light or if photocell520 receives too little light, the voltage at the movable contact ofpotentiometer 1200 will become sufiiciently positive to tend to causecurrent to flow through the diodes 1208 and 1214 and the base-emittercircuit of transistor 1030. That current would keep that transistorconductive even if the other two pairs of photocells received thecorrect amounts of light and even if the switch 790 was closed. Ifphotocell 518 receives too little light or if photocell 520 receives toomuch light, the transistor 1204 will become less conductive and thevoltage at the collector of that transistor will become sulficientlypositive to tend to cause current to flow through diode 1214 and thebase-emitter circuit of transistor 1030. The current would keep thattransistor conductive even if the other two pairs of photocells receivedthe correct amounts of light and even if the switch 790 was closed.

It will thus be apparent that the photocells 518 and 520, the transistor1204, and the diodes 1208 and 1214 coact to provide a dual action.Specifically, if those photocells cause the voltage at the movablecontact of potentiometer 1200 to become unduly positive, current willtend to flow through the diodes 1208 and 1214 and the base-emittercircuit of transistor 1030 and keep that transistor conductive. On theother hand, if those photocells make the voltage at the movable contactof potentiometer 1200 unduly negative, the transistor 1204 will make thevoltage at the collector thereof unduly positive; and current will tendto flow through diode 1214 and the base-emitter circuit of transistor1030 and keep the latter transistor conductive.

The resistors 788, 791, 966 and 967 will coact with the switch 790, thediode 1052, and the Schmitt trigger to serve as an inhibiting circuit.Specifically, that circuit will prevent energization of the relay coil624 until the switch 790 is closed even if all of the photocells 214,216, 218, 220, 518 and 520 are receiving the proper amounts of light.That inhibiting circuit is very useful because it will keep acombination or combinations of light and dark areas on a bill fromeffecting energization of the relay coil 624 prior to the time that billis fully moved into the testing area of the currency detector. Thediodes 1054, 1060, 1062, 1068, 1072 and 1074 also act as parts of thatinhibiting circuit, and they will prevent energization of the relay coil624 in the event any one of the photocells 214, 216, 218, 220, 518 and520 fails to receive the proper amount of light.

Whenever an authentic bill is disposed within the testing area of thecurrency detector, each of the photocells 214, 216, 218, 220, 518 and520 will receive some light, even though the photocells 216, 220 and 520will receive less light than the photocells 214, 218 and 518 willreceive. This is desirable because it means that if any one of the lamps206, 208, 210, 212, 514 and 516 does not become illuminated, theadjacent photocell will receive too little light and will coact with theinhibiting circuit to prevent the energization of the relay coil 624.This means that the burning out of one or more of the lamps will not beable to effect acceptance of a bill.

While potentiometers 972, 994 and 1014 are shown in FIG. 1, it would bepossible to use tapped resistors or other equivalent electricalcomponents in lieu of those potentiometers.

The connecting of the photocells in pairs, and the connecting of apotentiometer or equivalent electrical component in parallel with one ofthe photocells of each pair of photocells, enable the photocells toreceive light from any desired portions of a bill. For example, some ofthe photocells could be set to receive light from the lightest areas ofa bill while other of those photocells could be set to receive lightfrom the darkest areas of those bills, and still other photocells couldbe set to receive light from areas of intermediate lightness anddarkness.

The preferred embodiment of optical sensing system which is describedhereinbefore is intended to be used with a currency detector that willaccept authentic onedollar bills of the United States and will rejectall other bills. However, if desired, that optical sensing system couldbe adapted, by appropriate positioning of the lamps 206, 208, 210, 212,514 and 516 and by appro riate positioning of the photocells 214, 216,218, 220, 518 and 520 to sense other authentic bills of the UnitedStates and of foreign countries. While three pairs of photocells areused in the optical-sensing system of the present invention, more orfewer pairs of photocells could be used without any change in the basiccircuit. All that need be done to add further photocells is to provideanother potentiometer, another transistor and its associated resistors,and two additional diodes.

Whereas the drawing and accompanying description have shown anddescribed two preferred embodiments of the resent invention, it shouldbe apparent to those skilled in the art that various changes may be madein the form of the invention without affecting the scope thereof.

What We claim is:

1. A sensing system for a currency detector that comprises:

(a) a pair of photocells that are connected in series,

(b) a first potentiometer that has a movable contact and that isconnected in parallel with one of said photocells,

(c) a Schmitt trigger,

(d) a phase inverter which has the input thereof connected to saidmovable contact of said first potentiometer,

(e) a diode that is connected between the output of said phase inverterand the input of said Schmitt trigger,

(f) a second diode that is connected between said movable contact ofsaid first potentiometer and said input of said Schmitt trigger,

(g) a second pair of photocells that are connected in series,

(h) a second potentiometer that has a movable contact and that isconnected in parallel with one of said photocells of said second pair ofphotocells,

(i) a second phase inverter which has the input thereof connected tosaid movable contact of said second potentiometer,

(j) a third diode that is connected between the output of said secondphase inverter and the input of said Schmitt trigger,

(k) a fourth diode that is connected between said movable contact ofsaid second potentiometer and said input of said Schmitt trigger,

(1) said Schmitt trigger normally having the first section thereofconductive and normally having the second section thereofnon-conductive,

(In) said Schmitt trigger having a potentiometer that establishes thebias for said second section of said Schmitt trigger,

(n) a voltage divider,

(o) a switch that can change the effective resistance of said voltagedivider,

(p) a fifth diode between said voltage divider and the input of saidSchmitt trigger,

(q) a source of power that causes current to flow through each photocellof said pairs of photocells whenever said photocell is illuminated andthrough each of said potentiometers and through said voltage divider,that normally causes current to flow and conductively bias said firstsection of said Schmitt trigger after flowing through part of saidvoltage divider and said fifth diode or through part of the first saidpotentiometer and said second diode or through said part of the firstsaid potentiometer and the first said phase inverter and the first saiddiode or through part of said second potentiometer and said fourth diodeor through said part of said second potentiometer and said second phaseinverter and said third diode, and that can cause current to flowthrough said second section of said Schmitt trigger when the first saidsection of said Schmitt trigger becomes non-conductive,

(r) the first said pair of photocells and the first said potentiometercoacting, whenever an acceptable bill is not present, with said seconddiode or with the first said phase inverter and the first said diode totend to keep the first said section of said Schmitt trigger conductive,

(s) said second pair of photocells and said second potentiometercoacting, whenever an acceptable bill is not present, with said fourthdiode or with said second phase inverter and said third diode to tend tokeep the first said section of said Schmitt trigger conductive,

(t) said voltage divider and said fifth diode coacting, whenever anacceptable bill is not present, to tend to keep the first said sectionof said Schmitt trigger conductive,

(u) the first said pair of photocells and the first said potentiometercoacting, whenever an acceptable bill is present, with said second diodeand with the first said phase inverter and the first said diode to tendto render said first section of said Schmitt trigger non-conductive,

(v) said second pair of photocells and said second potentiometercoacting, whenever an acceptable bill is present, with said fourth diodeor with said second phase inverter and said third diode to tend torender said first section of said Schmitt trigger non-conductive,

(w) said voltage divider and said fifth diode coacting, whenever anacceptable bill is present to tend to render said first section of saidSchmitt trigger nonconductive,

(x) said first and second pairs of photocells being disposed adjacent atesting area,

(y) said switch and said diodes being parts of an inhibiting circuitthat will keep said first section of said Schmitt trigger conductiveuntil after an acceptable bill has been fully moved into said testingareas, and

(z) lamps that are illuminated continuously throughout the operation ofsaid sensing system and that cause light from inserted bills to pass tosaid photocells,

(aa) one of said photocells receiving substantially no light until abill is inserted and then receiving a substantial amount of light ifsaid bill is acceptable,

(ab) another of said photocells receiving substantially no light until abill is inserted and then receiving only a limited amount of light ifsaid bill is acceptable,

(ac) still another of said photocells receiving a substantial amount oflight until a bill is inserted and then receiving only a limited amountof light if said bill is acceptable.

2. A sensing system that comprises:

(a) a pair of sensing elements that are connected in series,

(b) a voltage divider that is connected in parallel with one of saidsensing elements,

(c) an actuatable device,

(d) a phase inverter which has the input thereof connected to a contactof said voltage divider,

(e) a member that is connected between said contact of said voltagedivider and said actuatable device and that can respond to a firstpredetermined voltage at said contact to actuate said actuatable device,and

(f) a second member that is connected between the output of said phaseinverter and said actuatable device and that can coact with said phaseinverter and with a second predetermined voltage at said contact toactuate said actuatable device,

(g) the first said and said second predetermined voltages being equal orclose to each other,

(h) the first said member responding to voltages displaced in onedirection from the first said predetermined voltage to prevent actuationof said actuatable device,

(i) said second member and said phase inverter responding to voltaegsdisplaced in the opposite direction from said second predeterminedvoltage to prevent actuation of said actuatable device,

(i) said sensing elements being photocells,

(k) said voltage divider being a potentiometer,

(1) said members being diodes.

3. A sensing system that comprises:

(a) a pair of sensing elements that are connected in series,

(b) a voltage divider that is connected in parallel with one of saidsensing elements,

(c) an actuatable device,

(d) a phase inverter which has the input thereof connected to a contactof said voltage divider,

(e) a member that is connected between said contact of said voltagedivider and said actuatable device and that can respond to a firstpredetermined voltage at said contact to actuate said actuatable device,and

(f) a second member that is connected between the output of said phaseinverter and said actuatable device and that can coact with said phaseinverter and with a second predetermined voltage at said contact toactuate said actuatble device,

(g) the first said and said second predetermined voltages being equal orclose to each other,

(h) the first said member responding to voltages displaced in onedirection from the first said predetermined voltage to prevent actuationof said actuatable device,

(i) said second member and said phase inverter responding to voltagesdisplaced in the opposite direction from said second predeterminedvoltage to prevent actuation of said actuatable device,

(j) said members being connected in series between said contact and saidactuatable device,

(k) said output of said phase inverter being connected to a junctionbetween said members.

4. A sensing system that comprises:

(a) a pair of sensing elements that are connected in series,

(b) a voltage divider that is connected in parallel with one of saidsensing elements,

(c) an actuatable device,

(d) a phase inverter which has the input thereof connected to a contactof said voltage divider,

(e) a member that is connected between said contact of said voltagedivider and said actuatable device and that can respond to a firstpredetermined voltage at said contact to actuate said actuatable device,and

(f) a second member that is connected between the output of said phaseinverter and said actuatable device and that can coact with said phaseinverter and with a second predetermined voltage at said contact toactuate said actuatable device,

(g) the first said and said second predetermined voltages being equal orclose to each other,

(h) the first said member responding to voltages displaced in onedirection from the first said predetermined voltage to prevent actuationof said actuatable device,

(i) said second member and said phase inverter responding to voltagesdisplaced in the opposite direction from said second predeterminedvoltage to prevent actuation of said actuatable device.

5. A sensing system for a currency detector that comprises:

(a) a photocell that is adjacent a testing area for bills,

(b) a lamp that is adjacent said testing area,

() means that can coact with said photocell to provide static sensing ofbills introduced into said sensing area and to provide an accept signalas an acceptable bill is fully moved into said testing area and comes torest,

((1) an inhibiting circuit that keeps said photocell and said means fromproviding an accept signal until after an acceptable bill has been fullymoved into said testing area,

(e) whereby said lamp can be illuminated continuously during the entiretime said currency detector is connected to a source of power and is incondition to accept bills,

(f) said inhibiting circuit including a plurality of diodes and a switchthat is open until after an acceptable bill has been fully moved intosaid testing position and that subsequently closes, and

(g) a second means to provide a further and different test of billsinserted into said testing area,

(h) said second means being adapted to respond to the insertion of anacceptable bill into said testing area to close said switch of saidinhibiting circuit, and thereby enable said photocell and the first saidmeans to provide an accept signal.

6. A sensing system for a currency detector that comprises:

(a) a photocell that is adjacent a testing area for bills,

(b) a lamp that is adjacent said testing area,

(0) means that can coact with said photocell to provide static sensingof bills introduced into said sensing area and to provide an acceptsignal as an acceptable bill has been fully moved into said testing areaand comes to rest, and

(d) an inhibiting circuit that keeps said photocell and said means fromproviding an accept signal until after an acceptable bill has been fullymoved into said testing area,

(e) whereby said lamp can be illuminated continuously during theoperation of said sensing system,

(i) said means including a flip-flop sub-circuit that has one sectionthereof held conductive until after an acceptable bill has been fullymoved .into said test- .ing position and that subsequently becomesnon-conductive,

(g) said inhibiting circuit being responsive to the absence of anacceptable bill to supply a voltage to said one section of saidflip-flop sub-circuit to hold said section conductive,

(h) said inhibiting circuit being responsive to the presence of anacceptable bill to provide another and different voltage to said onesection of said flipflop sub-circuit to tend to cause said section tobecome nonconductive.

7. A sensing system for a currency detector that comprises:

(a) a photocell that is adjacent a testing area for bills,

(b) a lamp that is adjacent said testing area,

(c) means that can coact with said photocell to provide static sensingof bills introduced into said sensing area and to provide an acceptsignal as an acceptable bill is fully moved into said testing area andcomes to rest,

((1) an inhibiting circuit that keeps said photocell and said means fromproviding an accept signal until after an acceptable bill has been fullymoved into said testing area,

(e) whereby said lamp can be illuminated continuously during the entiretime said currency detector is connected to a source of power and is incondition to accept bills, and

(f) a second means to provide a further and different test of billsinserted into said testing area,

( g) said second means being adapted to respond to the insertion of anacceptable bill into said testing area to disable said inhibitingcircuit, and thereby enable said photocell and the first said means toprovide an accept signal.

8. A sensing system for a currency detector that comprises:

(a) a pair of photocells that are connected in series,

(b) a first potentiometer that has a movable contact and that isconnected in parallel with one of said photocells,

(c) an actuatable device that has the input thereof connected to saidmovable contact of said potentiometer, and

(d) a second potentiometer that is connected to said actuatable deviceand that can .be adjusted to adjust the threshold value of saidactuatable device,

(e) the first said potentiometer being adjustable to establish a voltageat the input of said actuatable device which corresponds to anacceptable bill of predetermined cleanness and contrast,

(f) said first potentiometer being adjustable to establish a secondvoltage at the input of said actuatable device which is" displaced fromthe first said voltage by a predetermined amount and which correspondsto said acceptable bill and to acceptable bills having cleanness andcontrast that are different from said predetermined cleanness andcontrast,

(g) said second potentiometer being adjustable to set said thresholdvalue of said actuatable device at a level which will cause actuation ofsaid actuatable device Whenever a bill coacts with said photocells andthe first said potentiometer to establish the first said or said secondvoltage at said input of said actuatable device.

9. A sensing system for a currency detector that comprises:

(a) a pair of photocells that are connected in series,

(b) a first potentiometer that has a movable contact and that isconnected in parallel with one of said photocells,

(c) an actuatable device,

(d) a phase inverter which has the input thereof connected to saidmovable contact of said potentiometer,

(e) a member that is connected between that output of said phaseinverter and the input of said actuatable device,

(f) a second member that is connected between said movable contact ofsaid first potentiometer and said input of said actuatable device, and

(g) a second potentiometer that is connected to said actuatable deviceand that can be adjusted to adjust the threshold value of saidactuatable device,

(h) the first said potentiometer being adjustable to establish a voltageat the input of said actuatable device which corresponds to anacceptable bill of predetermined cleanness and contrast,

(i) said first potentiometer being adjustable to establish a secondvoltage at the input of said actuatable device which is displaced fromthe first said voltage by a predetermined amount and which correspondsto said acceptable bill and to acceptable bills having cleanness andcontrast that are difii'erent from said predetermined cleanness andcontrast,

(j) said second potentiometer being adjustable to set said thresholdvalue of said actuatable device at a level which will cause actuation ofsaid actuatable device whenever a bill coacts with said iphotocells andthe first said potentiometer to establish the first said or said secondvoltage at said input of said actuable device,

(k) said members and said phase inverter causing said sensing system torespond to unacceptable bills to ten-d to supply voltages to said inputof said actuatable device which will prevent actuation of saidactuatable device.

10. A sensing system that comprises:

(a) a pair of sensing elements that are connected in series,

(b) a voltage divider that is connected in parallel with one of saidsensing elements,

(c) an actuatable device,

(d) a phase inverter which has the input thereof connected to a contactof said voltage divider,

(e) a member that is connected between said contact of said voltagedivider and said actuatable device and that can respond to a firstpredetermined voltage at said contact to actuate said actuatable device,and

(f) a second member that is connected between the output of said phaseinverter and said actuatable device and that can coact with said phaseinverter and with a second predetermined voltage at said contact toactuate said actuatable device,

(g) the first said and said second predetermined voltages being equal orclose to each other.

11. A sensing system that comprises:

(a) a pair of sensing elements that are connected in series,

(b) a voltage divider that is connected in parallel with one of saidsensing elements,

(-c) an actuatable device,

(d) a phase inverter which has the input thereof connected to a contactof said voltage divider,

(e) a member that is connected between said contact of said voltagedivider and said actuatable device and that can respond to a firstpredetermined voltage at said contact to actuate said actuatable device,and

(f) a second member that is connected between the output of said phaseinverter and said actuatable device and that can coact with said phaseinverter and with a second predetermined voltage at said contact toactuate said actuatable device,

(g) the first said and said second predetermined voltages being equal orclose to each other,

(h) said sensing elements being photocells,

(i) said voltage divider being a potentiometer,

(j) said members being diodes.

12. A sensing system for a currency detector that comprises:

(a) a sensing element that can respond to an acceptable bill to developa voltage,

(b) a first voltage divider that has said voltage applied to it,

(c) an actuatable device that is connected to said voltage divider toenable and voltage divider to supply a voltage to said actuatabledevice, and

(d) a second voltage divider, that is connected to said actuatabledevice to determine the level of the voltage that must be supplied tosaid actuatable device to actuate said actuatable device,

(e) the first said voltage divider being adjustable to supply to saidactuatable device a voltage which corresponds to an acceptable bill of apredetermined cleanness and contrast,

(f) the first said voltage divider also being adjustable to supply tosaid actuatable device a further voltage which corresponds to saidacceptable bill and to an acceptable bill having a cleanness andcontrast different from said predetermined cleanness and contrast,

g) said second voltage divider being adjustable to set the level of thevoltage, that must be supplied to said actuatable device to actuate saidactuatable device at a level which will cause said actuatable device tobecome actuated when said further voltage is applied to it,

(h) said voltage dividers thereby enabling said sensing system toestablish adjustable ranges of cleanness and contrast for the bills tobe accepted by said sensing system.

13. A sensing system for a currency detector that comprises:

(a) a sensing means that can respond to the insertion of a bill into atesting area to develop a voltage,

(b) an actuatable device,

(c) a second means that is connected to said actuatable device and thatcan tend, whenever said voltage is a predetermined value, to causeactuation of said actuatable device,

(d) said second means tending, whenever said voltage is displaced in apredetermined direction from said predetermined value, to preventactuation of said actuatable device, and

(e) a third means that can tend, whenever said voltage is apredetermined value, to cause actuation of said actuatable device,

(f) said third means tending, whenever said voltage is displaced in theopposite direction from said predetermined value, to prevent actuationof said actuatable device,

(g) whereby said second and said third means cause said sensing systemto reject bills that cause said sensing means to develop to high or toolow a voltage,

(h) said second and said third means being static elements that permitonly unidirectional How of current therethrough.

14. A sensing system for a currency detector that comprises:

(a) a sensing means that can respond to the insertion of a bill into atesting area to develop a voltage,

(b) an actuatable device,

(5) a second means that is connected to said actuatable device and thatcan tend, whenever said voltage is a predetermined value, to causeactuation of. said actuatable device,

(d) said second means tending, whenever said voltage is displaced in apredetermined direction from said predetermined value, to preventactuation of said actuatable device, and

(e) a third means that is connected to said actuatable device and thatcan tend, whenever said voltage is a predetermined value, to causeactuation of said actuatable device,

(f) said third means tending, whenever said voltage is displaced in theopposite direction from said predetermined value, to prevent actuationof said actuata ble device,

(g) said third means including a phase inverter.

UNITED STATES PATENTS Shepard 250209 Burtner et a1. 250219 Timms 250219Goodman et a1. 2502'14 X Bookout et a1.

Zuck et a1. 250209 RALPH G. NILSON, Primary Examiner.

WALTER STOLWEIN, Examiner.

3. A SENSING SYSTEM THAT COMPRISES: (A) A PAIR OF SENSING ELEMENTS THATARE CONNECTED IN SERIES, (B) A VOLTAGE DIVIDER THAT IS CONNECTED INPARALLEL WITH ONE OF SAID SENSING ELEMENTS, (C) AN ACTUATABLE DEVICE,(D) A PHASE INVERTER WHICH HAS THE INPUT THEREOF CONNECTED TO A CONTACTOF SAID VOLTAGE DIVIDER, (E) A MEMBER THAT IS CONNECTED BETWEEN SAIDCONTACT OF SAID VOLTAGE DIVIDER AND SAID ACTUATABLE DEVICE AND THAT CANRESPOND TO A FIRST PREDETERMINED VOLTAGE AT SAID CONTACT TO ACTUATE SAIDACTUATABLE DEVICE, AND (F) A SECOND MEMBER THAT IS CONNECTED BETWEEN THEOUTPUT OF SAID PHASE INVERTER AND SAID ACTUATABLE DEVICE AND THAT CANCOACT WITH SAID PHASE INVERTER AND WITH A SECOND PREDETERMINED VOLTAGEAT SAID CONTACT TO ACTUATE SAID ACTUATABLE DEVICE, (G) THE FIRST SAIDAND SAID SECOND PREDETERMINED VOLTAGES BEING EQUAL OR CLOSE TO EACHOTHER, (H) THE FIRST SAID MEMBER RESPONDING TO VOLTAGES DISPLACED IN ONEDIRECTION FROM THE FIRST SAID PREDETERMINED VOLTAGE TO PREVENT ACTUATIONOF SAID ACTUATABLE DEVICE, (I) SAID SECOND MEMBER AND SAID PHASEINVERTER RESPONDING TO VOLTAGES DISPLACED IN THE OPPOSITE DIRECTION FROMSAID SECOND PREDETERMINED VOLTAGE TO PREVENT ACTUATION OF SAIDACTUATABLE DEVICE,